Various implantable devices exist for delivering infusate, such as medication, to a patient. One such device is an implantable valve accumulator pump system. This system includes an electronically controlled metering assembly located between a drug reservoir and an outlet catheter. The metering assembly may include two normally closed solenoid valves that are positioned on the inlet and outlet sides of a fixed volume accumulator. The inlet valve opens to admit a fixed volume of infusate from the reservoir into the accumulator. Then, the inlet valve is closed and the outlet valve is opened to dispense the fixed volume of infusate from the accumulator to an outlet catheter through which the infusate is delivered to the patient. The valves may be controlled electronically via an electronics module, which can optionally be programmed utilizing an external programmer to provide a programmable drug delivery rate. The metering assembly is designed such that the inlet valve and the outlet valve are never simultaneously open.
This type of implantable infusion device is highly effective in most situations. However, when a patient with such a device enters an MRI (magnetic resonant imaging) machine and the machine is activated, the large magnetic fields may affect the operation of the pump's valves which could cause the metering function of the accumulator to be bypassed. In some cases, the inlet and outlet valves of the pumps may open simultaneously, creating a severe safety risk for the patient. Consequently, patients implanted with these devices must be instructed to have the pump reservoir emptied before undergoing an MRI procedure. This prohibition and warning is commonplace for patients implanted with such medical devices. Requiring implanted medical devices to be emptied before an MRI procedure adds to the cost of the procedure and may delay the procedure.